1. Field of the Invention
This invention relates to an ultrasonic blood velocity detector using the Doppler shifts.
2. Description of the Prior Art
Blood velocity can be detected by measuring the Doppler shifts in frequency imparted to ultrasound by reflection from moving red blood cells. There are various ultrasonic blood velocity detectors using such a Doppler method.
"New ultrasonic diagnostic technique", Clinical Ultrasonic Wave Series 9, published in 1984, page 86, discloses one example of such an ultrasonic Doppler blood velocity detector. This prior art detector uses high pass filters in separating blood velocity Doppler signals and clutter signals caused by motions of internal organs within an examined body. It should be noted that the clutter signals decrease the accuracy of the measurement of the blood velocity. In the prior art detector, when a low blood velocity is measured, the clutter signals are close to the blood velocity Doppler signals in frequency so that the high pass filters tend to inadequately separate the blood velocity Doppler signals and the clutter signals. The inadequate separation results in a decreased accuracy of the measurement of the blood velocity.